The present invention relates to a UV-A, UV-B discrimination sensor for measuring the presence or absence and intensity of UV rays, as well as for distinguishing between long and medium wave length UV rays.
Light waves from the sun which reach the earth are divided into infrared rays, visible light rays and UV rays on the basis of the region of-the wavelength. In terms of total energy released from the sun, infrared rays comprise 42%, visible light rays comprise 52% and UV rays comprise 6%. However, in terms of the energy of the light, as compared to infrared and visible light rays, UV rays have the larger effect on living organisms.
In terms of biological effects, UV rays may be categorized into three different types: long wavelength UV rays (UV-A: 320.about.400nm), medium wavelength UV rays (UV-B: 280.about.320 nm) and short wavelength UV rays (UV-C: 190.about.280 nm). Of these, UV C rays are absorbed by the ozone layer which surrounds the earth and do not reach the earth's surface. UV-A and UV-B rays reach the earth's surface and are well known to bring about a number of effects. (see "Chemistry and Chemical Industry," vol. 40, no. 6, page 467 (1987)).
UV rays cause suntanning in humans. However, depending on the type of UV ray, suntanning is caused in different ways and may be divided into the following two categories.
Long wavelength UV-A causes skin darkening only, thereby producing a suntanned appearance. The long wavelength UV-A rays also directly participate in the formation of vitamin D and generally have positive effects on human beings. In contrast however, the short wavelength UV-B rays cause blotting and freckling of the skin, and cause blistering and sunburn (sunburn damage extends several layers deep); UV-B therefore has deleterious effects on human beings. It is particularly easy to be effected by UV-B while performing open air activities at, for example, the beach or mountains. Even if activities such as going to the beach, where UV rays are especially strong, are avoided, suntanning nevertheless occurs on a daily basis.
The quantity of UV increases greatly during the period from spring to summer, and is during this time two to three times greater than when the quantity of UV is at its minimum (in December). Additionally, on a daily basis, the quantity of UV peaks during the hours of 11 in the morning to 2 in the afternoon. Moreover, because UV rays reach the earth's surface even on overcast days, and because the quantity of UV-A does not change significantly between cloudy days and clear days, it is difficult to estimate directly the quantity of UV from the brightness of the light.
Accordingly, there are two types of sun protection formulations, or so-called anti-sunburn cosmetic preparations, utilized as protective measures against sunburning, one type being for prevention of both suntan and sunburn, and the other type being for obtaining an attractive suntan while preventing sunburn. Used as the latter are formulations referred to as "UV-B sun protection formulations" which absorb only UV-B, allowing penetration of UV-A. Used as the former are sun protection types which absorb both UV-A and UV-B, however more numerous are sun protection types referred to as "UV-A sun protection formulations" which primarily absorb UV-A, and types which prevent both suntanning and sunburning by combination with a UV-B sun protection formulation.
If the light quantity of UV-A and UV-B rays can be measured, then the above types of sun protection formulations can be appropriately utilized, making it possible to take effective countermeasures against sunburn.
Moreover, due to detection of the ozone hole in recent years, it has been pointed out that there is a damage of an increase in the number of cases of skin cancer. If the ozone hole grows larger, or, even if the ozone hole does not grow larger but the thickness of the ozone layer decreases, there will, in proportion to this, be an increase in the light quantity of UV-B. In terms of harmful effects on human beings, .about.305 nm UV ray, which falls in the UV-B region, destroys the genetic material, DNA, with the result being that there is an increased risk of developing skin cancer. The light quantity of UV-A and UV-B are not proportional and it is not possible to directly predict UV-A light quantity and UV-B light quantity from the combined total of UV light quantity. Further, neither is the amount of cloud cover in the sky and the total UV quantity proportional; accordingly, it is dangerous to neglect taking appropriate countermeasures in regard to UV exposure merely for the reason that the sky is clouded over.
UV sensors have recently been marketed as a means to conveniently measure the presence or absence and intensity of UV. In such types of UV sensors, a composition such as a photochromic compound which displays a change upon exposure to UV is soaked into a binder of, for example, paper. When the UV sensor is held aloft, the presence or absence and the intensity of the UV may be measured by the amount of change in color or color density.
Further, as a suntanning sensor, a sensor which eliminates the effects from visible and infrared light and measures UV-A and UV-B has been developed (see: sales catalogue for Toray Techno. Co., Ltd.). This type Of Uv Sensor is very expensive.
As was stated above, there are two types of UV, UV-A and UV-B, which reach the earth's surface from the sun, however, conventional UV sensors were not able to distinguish between UV-A and UV-B. It is therefore not possible to discern whether the presence or intensity of the UV measured was due to UV-A, UV-B or to a combination of both.
Accordingly, without being able to judge whether only suntanning would occur, or whether suntanning accompanied by sunburning would occur, it was difficult to decide upon effective countermeasures to avoid UV exposure.
As it was not possible for the simple conventional UV sensors to distinguish between UV-A and UV-B, it was necessary to combine a diffraction grating or interference filter with a light quantity meter.
There have been developed, for example, multi-band UV light quantity meters and illuminance meters which, rather than being utilized to measure the UV in sunlight, have instead applications related to the industrial use of UV such as, for example, application primarily as a monitor to monitor UV quantity for an UV curable resin. Such multi-band UV light quantity meters and illuminance meters can distinguish between UV-A waves for which the wave length is 320 nm to 400 nm, and UV-B waves, for which the wave length is 270 nm to 310 nm. (see sales catalogue of Orc Manufacturing Co., Ltd.). Moreover, also available as compact and handy devices are thin-type UV light quantity meters. These are sensors which measure only a portion of UV-A, from wave lengths of 320 nm to 390 nm.
Such UV-A, UV-B discriminating sensors have a structure wherein a junctional semiconductor device is used as the sensor portion and a band pass filter is attached to the light intake portion.
UV sensors and UV-A, UV-B discriminating sensors are both light sensors which utilize semiconductor devices and are designed to exhibit sensitivity to UV. The discrimination or selection of UV is carried out by a band pass filter for use in optics which is attached to the sensor window. Accordingly, it is necessary to include an electronic circuit which is capable of displaying the output photocurrent on a meter or display. For this reason, conventional UV sensors all require a certain thickness (greater than several millimeters) and size (greater than several centimeters). Moreover, also necessary to operate these is an electric source.
Conventional sensors therefore required large-scale devices, electricity to drive these devices and special expertise. Moreover, from an economical point of view, such devices are very expensive. For these reasons, therefore, the development of a convenient UV-A, UV-B discriminating sensor capable of distinguishing between UV-A and UV-B was strongly desired.
The object of the present invention is to provide a convenient UV-A, UV-B discriminating sensor which can easily discriminate between the presence or absence and quantity of UV-A and UV-B, and for which no special expertise or special devices are required.